What is the principle that states that living species are descended from ancient ones?

The principle that states that living species are descended from ancient ones is known as "descent with modification," a key concept in evolutionary theory. This principle, articulated by Charles Darwin, suggests that species evolve over time through processes such as natural selection and genetic variation, leading to the diversity of life observed today. It underscores the idea that all living organisms share a common ancestry, connecting them through a vast evolutionary tree.